High Arctic observations of strato-mesospheric temperatures and gravity wave activity

Duck, T. J., Ph. D. Thesis, York University, Toronto, 174 pages, 1999.

Abstract. Over four hundred nights of temperature and internal gravity wave measurements were obtained in the middle atmosphere by a lidar (laser radar) stationed in the Canadian High Arctic at Eureka (80N, 86W) during the winters of 1992/93 to 1997/98. These observations are particularly interesting due to the influence over Eureka of the Arctic stratospheric vortex, an enormous cyclone that dominates the wintertime stratospheric circulation. It is within the lower stratosphere of the vortex core that (temperature sensitive) ozone depletions are found. Movements of the vortex have allowed measurements from Eureka to be obtained inside the vortex core, within the vortex jet, and outside of the vortex altogether. The observations have shown that temperatures in the lower (upper) stratosphere of the vortex core are very cold (warm), and vice versa for measurements obtained outside of the vortex altogether. By examining temperature measurements inside the vortex core only, an unexpected strong annual warming of the upper stratosphere was found. The warming commenced on average in late December and propagated down to levels below 30 km in altitude. A smaller but significant cooling was apparent in the lower mesosphere at the same time. The measurements of gravity wave activity revealed low gravity wave energies both inside the vortex core and outside of the vortex altogether. Episodes of high gravity wave activity were only seen in the vortex jet after late December and ended with the vortex breakdown in late March / early April. It is proposed, and supported by simple calculations, that the late December elevation in gravity wave activity within the vortex jet drove the concurrent intra-vortex stratospheric warming; i.e, that increased turbulent gravity wave dissipation near the stratopause forced flow into the vortex centre which compressed and adiabatically warmed the stratospheric airmass. The variations in gravity wave activity with respect to vortex position and time of year are related to stratospheric wind speeds and critical level filtering. These observations have implications for our understanding of sudden stratospheric warming events and the ozone depletion problem.

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